This invention relates to metal founding and more particularly to centrifugal casting in which the molten material is impelled radially outwardly against the forming surface by rotation of the surface.
Many cylindrical parts such as cast iron pipes, tubular casting, bearings, and the like, are manufactured by utilizing the casting process known as centrifugal casting. Although this basic process has proven highly effective for mass production of cylindrical parts, one of the difficulties encountered therewith has been that of controlling the microstructure of the casting particularly when the casting is made of cast iron. The physical properties and microstructure of cast iron are controlled by adding a variety of treatment materials to the molten base metal.
One method of adding treatment materials to molten iron is by the batch process where a measured amount of a treatment agent is thrown into the molten iron within the ladle prior to pouring the molten iron into the mold. However, the effect of treatment agents is time dependent and tends to fade immediately after mixing with the molten iron. Thus, even if a slight delay in the pouring process occurs, the effect of treatment agents is lost and the resulting casting will not have the proper microstructure.
Another method of adding the treating agent to the molten iron consists of feeding a treatment agent in powder form from a hopper into a stream of molten iron flowing through a pouring channel and into a mold. However, one of the problems associated with treating agents in bulk or powdered form is that they tend to pick up moisture both in storage and in use. If the treating agent is not kept dry the moisture tends to create pin holes in the resulting cavity. Also, the environment in which the powdered treating agent is kept tends to promote caking of the treating agent in the hopper, making accurate metering of the treating agent from the hopper difficult to control. Also, uneven distribution causes partial or incomplete dissolution such that inclusions remaining are detrimental to the quality of the completed product.